It is desirable to increase the dietary intake of many beneficial nutrients. Particularly beneficial nutrients include fatty acids such as omega-3 and omega-6 long chain polyunsaturated fatty acids (LC-PUFAs) and esters thereof. Omega-3 PUFAs are recognized as important dietary compounds for preventing arteriosclerosis and coronary heart disease, for alleviating inflammatory conditions and for retarding the growth of tumor cells. Omega-6 PUFAs serve not only as structural lipids in the human body, but also as precursors for a number of factors in inflammation, such as prostaglandins and leukotrienes. Long chain omega-3 and the omega-6 PUFAs represent important classes of PUFAs.
There are two main series or families of LC-PUFAs, depending on the position of the double bond closest to the methyl end of the fatty acid: the omega-3 series contains a double bond at the third carbon, while the omega-6 series has no double bond until the sixth carbon. Thus, docosahexaenoic acid (“DHA”) has a chain length of 22 carbons with 6 double bonds beginning with the third carbon from the methyl end and is designated “22:6 n-3”. Other important omega-3 LC-PUFAs include eicosapentaenoic acid (“EPA”), which is designated “20:5 n-3,” and omega-3 docosapentaenoic acid (“DPA n-3”), which is designated “22:5 n-3.” Important omega-6 LC-PUFAs include arachidonic acid (“ARA”), which is designated “20:4 n-6,” and omega-6 docosapentaenoic acid (“DPA n-6”), which is designated “22:5 n-6.”
Because humans and many other animals cannot directly synthesize omega-3 and omega-6 essential fatty acids, they must be obtained in the diet. Traditional dietary sources of PUFAs include vegetable oils, marine animal oils, fish oils and oilseeds. In addition, oils produced by certain microorganisms have been found to be rich in LC-PUFAs. The oils derived from each of these sources, however, also contain substantial levels of saturated fatty acids and other undesirable impurities.
Numerous methods have been used to isolate or purify PUFAs and derivatives thereof from crude oils. Among these processes are fractional crystallization at low temperatures, urea adduct crystallization, extraction with metal salt solutions, super critical fluid fractionation on countercurrent columns and high performance liquid chromatography.
The increased use of PUFAs and esters thereof in the fields of medicine and nutrition has created a commensurate need for PUFAs that are concentrated and free of impurities. Previous efforts directed to purifying PUFAs, however, have suffered from problems such as high costs and decreased yields due, in part, to the use of harsh reagents. Accordingly, there is a need for improved methods of isolating and purifying PUFAs in a form that can be consumed and utilized by humans and other animals.